Subject: Re: [GIT PULL] AlacrityVM guest drivers for 2.6.33

From: Gregory Haskins <[email-masked]>
Date: Tue, 22 Dec 2009 14:15:38 -0500

On 12/22/09 1:53 PM, Avi Kivity wrote:
> I asked why the irqfd/ioeventfd mechanisms are insufficient, and you did not reply.
> 

BTW: the ioeventfd issue just fell through the cracks, so sorry about
that.  Note that I have no specific issue with irqfd ever since the
lockless IRQ injection code was added.

ioeventfd turned out to be suboptimal for me in the fast path for two
reasons:

1) the underlying eventfd is called in atomic context.  I had posted
patches to Davide to address that limitation, but I believe he rejected
them on the grounds that they are only relevant to KVM.

2) it cannot retain the data field passed in the PIO.  I wanted to have
one vector that could tell me what value was written, and this cannot be
expressed in ioeventfd.

Based on this, it was a better decision to add a ioevent interface to
xinterface.  It neatly solves both problems.

Kind Regards,
-Greg